In commercial motor vehicle engines with a heat storage device, the capacity of the heat storage device is usually equal to the coolant volume of the engine, for example, two liters. Here, the coolant volume of the engine denotes the volume that is taken up by the coolant in a design without coolant accumulator. At the time of starting of the engine, the hot coolant flows due to the action of a coolant pump from the heat storage device into the cold engine. At the same time, the cold coolant flows out of the engine into the heat storage device, where it remains for the time being. In this context, the term coolant exchange is used. The supplied hot coolant then circulates exclusively under the action of the coolant pump between the engine and the heat exchanger. As a result of this coolant exchange, the stored heat quantity is dissipated into the cold engine and via the heat exchanger into the interior of the vehicle, and as a result, the time that it takes to reach the operating temperature is shortened, and comfort of the vehicle occupants is achieved earlier.
After the engine has warmed up, the cold coolant from the accumulator is gradually mixed, by appropriate switching of a control valve, with the hot coolant in the engine. Optionally, superheated coolant is led through the cooler and cooled there. If the engine is switched off after a sufficiently long operating period, the coolant in the engine, heat exchanger and heat storage device is brought to the same temperature. During the subsequent operating pause, the coolant in the heat storage device maintains its temperature approximately, while the coolant in the engine and in the heat exchanger together with these components cools rapidly.
In spite of the above-described improvements, there is still the desire for and thus the problem of further reducing the emissions associated with the cold start and improving the heating comfort. A heat storage device is sought that more quickly and efficiently heats a cold engine upon starting.